Phalanx bones

Illustration of the phalanges

The phalanges in a human hand

In anatomy, phalanx bones (plural phalanges) are those that form the fingers and toes. In primates such as humans and monkeys, the thumb and big toe have two phalanges, while the other fingers and toes consist of three. Phalanges are classified as long bones.

The phalanges do not really have individual names but are named after the digit, and their distance from the body.

• Distal phalanges: are at the tips of the fingers and toes.
• Proximal phalanges: are closest to the hand (or foot) and articulate with the metacarpals of the hand, or metatarsals of the foot.
• Middle or intermediate phalanges: are between the distal and proximal. The thumb and big toe do not have middle phalanges.

The term phalanx or phalanges refers to an ancient Greek army formation in which soldiers stand side by side, several rows deep, like an arrangement of fingers or toes.

Phalangeal formula

The number of phalanges in animals is often expressed as a phalangeal formula, that indicates the numbers of phalanges in digits (beginning from medial). Primitive reptiles typically had the formula 2-3-4-5-3, and this pattern, with some modification, remained in many later reptiles and in the mammal-like reptiles. Primitive mammals, however, evolved feet with the formula 2-3-3-3-3, which remains in humans, among many other mammalian species. Modifications from this general mammalian pattern have almost always involved a reduction in the number of toes, although usually not in the number of phalanges within the toes. For example, the phalangeal formula of a deer is 3-3. Cetaceans are unusual among mammals, in that their flippers contain a considerably increased number of phalanges in the central digits, leading to phalangeal formulae such as 2-12-8-1.^[1]

References

• MedTerms.com Medical Dictionary

See also

• Phalanges of the foot
• Phalanges of the hand